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Associated Press photo

This 2008 photo provided by Glacier National Park shows Sperry Glacier, which has receded and separated into fragments.(Full-size photo)

GREAT FALLS – Healthy snowpack and cooler summers over the past four years have slowed melting of remaining glaciers in Glacier National Park in Montana, according to the U.S. Geological Survey.

“So the glaciers have paused in active retreat,” said Dan Fagre, a research ecologist with the USGS’ Northern Rocky Mountain Science Center in Bozeman who is stationed at Glacier.

But Fagre anticipates the glaciers, which are receding or disappearing, will likely resume retreating this year, if a forecast for El Niño-induced warmer temperatures comes to pass later this summer.

“This year we expect that any of the advantages the glaciers gained from the weather from the past few years will probably be erased,” he said.

Fagre and other researchers studying glaciers in the park plan to return Wednesday to Sperry Glacier, which is in the center of the park south of Logan Pass.

Sperry also is at the center of USGS’ efforts to monitor shrinking glaciers, and considered a benchmark for all of the park’s remaining glaciers.

“So what Sperry does, most of the other glaciers are doing as well,” Fagre said.

A glacier is a body of snow and ice that moves. It forms when winter snowfall exceeds summer melting and retreats when melting outpaces accumulation of new snow.

“We’ve had a warming trend here that is about 1.8 times greater than the rest of the global average and that’s enough to tip the balance for our glaciers,” Fagre said.

In 1850, there were an estimated 150 glaciers of that size, compared to 25 today that are least 25 acres in size.

At Glacier, researchers take photographs of glaciers and compare them to historic photos to map declines in the size.

In the 10 years of the monitoring of Sperry, there has been a 5 percent decline in volume.

“We had this sort of pause,” Fagre said of shrinking at Sperry Glacier and, by extrapolation, other glaciers. “They pretty much got as much snow as they needed.”

A recent paper showed trout hybridization has increased due to warming stream temperatures, which reflects a loss of snowpack in glaciers, Fagre said. Its lead author was USGS researcher Clint Muhlfeld.

“It affects the whole ecosystem,” Fagre said of receding glaciers. “And that’s a clear example of those effects.”

The park’s relatively small alpine glaciers are good indicators of climate, the long-term average of daily weather conditions, according to the USGS. While occasional big winters or frigid weeks may occur, the glaciers are melting as long-term mean temperatures increase, the agency says.